1. Technical Field
The present invention relates to a physiological sound examination device which estimates a state of a living body by obtaining a physiological sound of the living body and performing signal processing on the obtained physiological sound.
2. Background Art
In a hospital or the like, a doctor listens to a physiological sound of a patient, such as heart sound or lung sound, using a stethoscope to make a diagnosis. The diagnosis by auscultation is based on a subjective evaluation of the doctor. On this account, skill is required to make a correct diagnosis.
The lung sound refers to all sounds, except for sounds coming from the cardiovascular system, generated by the motion of breathing in the lungs and thorax regardless of whether normal or abnormal. Moreover, the lung sound is divided into a breath sound and an adventitious sound. The breath sound refers to a physiological sound whose source is airflow occurring in the respiratory tract by breathing. The adventitious sound refers to an abnormal sound, such as wheezing or pleural friction rub, caused in a pathological state. The sound source of breathing is thought to be in the respiratory tract which is relatively large.
Pneumothorax is one of lung diseases. Pneumothorax is an air space formed between the lung and the chest wall, and appears as a decrease in breath sound intensity in physical presentation. A method of detecting a state of pneumothorax has been disclosed (see PTL 1). More specifically, in this method, a sound wave is emitted from a speaker into the mouth and the trachea so that the emitted sound wave propagates through the body of the patient, and then the propagated sound wave is measured on the chest wall for signal processing.
With this method, a transfer function is calculated from the sound wave to be emitted and the sound wave measured on the chest wall, and an energy ratio between a low frequency band and a high frequency band is calculated using the transfer function. In this way, the state of pneumothorax is detected.
Moreover, as a method without emitting a sound wave from a speaker, PTL 1 also discloses a method of analyzing the lung sound measured on the chest wall. In this method, frequency conversion is performed using a lung sound signal detected on the chest wall, and an energy ratio between a low frequency band and a high frequency band is calculated. In this way, a respiratory state is detected.
Here, for making a respiratory diagnosis, the doctor listens to the lung sound by placing a stethoscope on different positions of the body. A device which includes, in order to detect a measurement position of the lung sound, an acceleration sensor in a sensor for measuring the lung sound has been disclosed (see PTL 2).
With this device, output values of the acceleration sensor are integrated to calculate a moving distance of the sensor, so that the measurement position of the lung sound is automatically detected.
Furthermore, when a patient is in a remote area, a person other than the doctor places a microphone on a predetermined position of the body of the patient to measure the physiological sound and then transmits the measured physiological sound via a wired or wireless communication to the doctor who thus listens to the physiological sound to make a diagnosis.
In order for the doctor to be able to make a diagnosis even when the microphone is not placed on the predetermined position of the body of the patient, a device whereby more than one microphone is placed on the body of the patient to help the doctor make the diagnosis has been disclosed (see PTL 3).
With this device, a weighted sum is calculated using acoustic signals received from the microphones, so as to simulate an acoustic signal corresponding to a position where no microphone is placed. In this way, a diagnosis made in a remote area is supported.